The invention concerns thermoplastically workable polyurethane-elastomers from substantially pure trans-1,4-cyclohexane-diisocyanate, short-chain diols and macrodiols, processes for the production of these elastomers as well as their use.
It has been known for a long time to call upon polyurethanes as the basis for the production of elastic materials. Such polyurethane-elastomers are formed through polyaddition of diisocyanates, predominantly methylene-bis-(4-phenylisocyanate), long-chain dihydroxy compounds, called "macrodiols", and lower-molecular dihydroxy- or diamino-compounds, the function of which is to act as chain lengthener.
Elastomers which have been formed by the use of diamino-compounds as chain lengtheners are designated, correspondingly, polyureaurethane.
Processes for the production of these polyurethanes are so fashioned that the macromolecule will display a suitable segment structure, composed of crystalline and amorphous blocks constructed in a certain arrangement. These blocks are referred to as hard segments and soft segments, respectively. Whereas the hard segments, based upon their crystalline characteristics, function as network fix points, the soft segments, upon use temperatures above their glass transition temperature, are responsible for the uncoiling characteristics of the elastomer (see e.g. "Textilpraxis International" 36 (1981), pages 839-844; "Entwicklungstendenzen auf dem Gebiet von Polyurethan-Elastomerfasern").
In order to produce, for example, elastomer fibers from these polyurethanes or polyureaurethanes, they are generally spun from their solutions. A spinning according to the melt-spinning technique, particularly economical and to be performed with high discharge velocities, at the same time environmentally compatible, is less suitable for the production of usable elastomer fibers.
It follows from e.g. Textilpraxis International 36 (1981), page 841, lines 39-46, that the urea groups--as elastomer-hard segment--cannot be melted without simultaneous decomposition, and they therefore are not generally obtained by means of melt-spin techniques. Moreover, thermoplastic polyurethane-elastomers with urethane hard segments have stabilities that are very low, no longer tolerable for the working-up into textiles.--The practical usefulness of those polyurethane-elastomer fibers constructed from aromatic diisocyanates, customarily short-chain diols and macrodiols, is thus limited, for example, in that they do not withstand the thermal loading occurring upon thermal fixation, dyeing, washing and ironing, on account of their low melt temperatures.--This applies in particular measure when these polyurethanes are constructed from aliphatic, instead of aromatic, diisocyantes.
As follows, moreover, from Lenzinger Berichte 45 (1978), 40, left column, last paragraph, polyureaurethanes cannot be worked up according to the melt-spin technique, but only according to the uneconomical dry-spinning or reaction-spinning processes. For the production of elastomer fibers, in practice these polyureaurethanes have carried through with diamines as chain lengtheners opposite polyurethanes with diols as chain lengtheners, since they display high hard segment melting points as well as excellent mechanical-elastic characteristics based upon a greater number of hydrogen bridge connections. These are conditioned, however, on simultaneously high melt temperatures, and are no longer stable in relation to the urea groups.
This disadvantage applies also for non-fading, i.e. fast-to-light, elastomer fibers from aliphatic diisocyanates, such as are described, e.g., in DE-OS No. 1,955,725. (Disclosure of polyureaurethanes, which are produced with cis/trans-mixtures of 1,4-cyclohexanediisocyanate and cycloaliphatic diamines as chain lengthener, and are worked up by means of solution spinning.)
Finally, in DE-OS No. 2,829,199, particularly valuable polyurethanes are described, which are obtained with the employment of practically pure trans-1,4-cyclohexanediisocyanate. These short, highly symmetrical, rigid diisocyanate molecules lead to a hard segment construction with higher order, higher hydrogen bridge connection density and crystallinity. The polyurethanes or polyureaurethanes distinquish through a particularly distinctly marked separation of the hard and soft segment blocks. Dependent upon this, they have low glass transition temperatures, particularly high softening temperatures, as well as excellent mechanical-elastic characteristics. Thermoplastically workable polyurethanes are also described. Useful fibers are, however, only obtained through spinning from solution, since under the various thermoplastic working-up processes, preparation by spinning from the melt is a special case characterized by long dwell times for the polymers in the high temperature range of the apparatus, high occurring shearing forces in the filters and nozzle, and low, required melt viscosities, to which particular requirements the thermoplastic polymer material is not equal too.